Surgical Treatment of Benign Bone Lesions

Chapter 148 Surgical Treatment of Benign Bone Lesions




Benign bone lesions about the knee are relatively common entities. These lesions can be a cause of pain, deformity, and emotional distress. Often, the treatment of these lesions is straightforward, with little associated morbidity.7 The knee is an extremely common location for most benign bone tumors. They present in a variety of ways, from incidental findings on radiographs to pain and deformity. A thorough clinical and radiographic evaluation of the patient with a bone lesion is critical (see Chapter 147). This chapter focuses on the surgical treatment of the common benign bone lesions about the knee for the general orthopedic surgeon as well as for the musculoskeletal oncologist.




Treatment of Specific Benign Conditions


The treatment of benign neoplasms about the knee of bone is based on the resultant symptomatology. Most benign bone lesions about the knee can be observed if they do not cause pain, deformity, cosmetic concern, functional disability, or increased risk of pathologic fracture. Mechanical irritation outside of the joint itself is a common cause for elective surgical treatment of tumors in this location. Benign bone lesions rarely cause internal derangement of the knee, with the rare exception of chondroblastomas and osteoid osteomas. This section describes the presentation, natural history, and treatment of the most common types of benign bone tumors about the knee.



Benign Bone-Forming Tumors



Osteoid Osteoma


The most common benign bone-forming tumor is the osteoid osteoma, accounting for 10% of all benign bone tumors. It is more common in males than in females, with the peak incidence in the second decade of life. With regard to the knee, the proximal femur is the most common location, although it can also arise in the distal femur, proximal tibia, and fibula. Dull aching pain is the most frequent symptom. Previously, some investigators believed that an osteoid osteoma was an inflammatory process such as a Brodie’s abscess, which has a somewhat similar clinical and radiographic appearance. Currently, it is accepted that an osteoid osteoma is a true osteoid-forming neoplasm, without histologic evidence of lymphocytes or plasma cells. Histologically, the nidus demonstrates aggressive but benign woven bone formation, with large numbers of osteoblasts and osteoclasts in a vascular fibrous stroma. No chondroid areas are seen.


The characteristic radiographic feature of an osteoid osteoma is a central lytic nidus that can measure up to 1 cm in diameter. In the common cortical lesion (Fig. 148-1), there will be an extensive reactive sclerosis creating a fusiform bulge on the bone surface. If the nidus is more centrally located in metaphyseal bone, less sclerosis is seen and the radiographic appearance is less diagnostic. Technetium bone scans are invariably positive. A computed tomography (CT) scan is helpful to locate the lesion better anatomically for improved preoperative planning.5 Magnetic resonance imaging (MRI) may miss the nidus, making establishment of the diagnosis more difficult.28




Osteoid osteomas have been attributed to otherwise unexplainable knee pain.29,41 If the nidus is close to a joint or within the joint, which can occur in approximately 15% of cases,3,45 inflammatory synovitis may result. This synovitis may inappropriately suggest the diagnosis of pyarthrosis or rheumatoid arthritis.85 If the bony reaction is focal and intense, the lesion can take on the appearance of an exostosis.55 Furthermore, an osteoid osteoma can mimic pes anserinus syndrome, when the lesion is located medially in the proximal tibia.72


Generally, symptoms are relieved with nonsteroidal anti-inflammatory drugs (NSAIDs) secondary to a high concentration of prostaglandins in the nidus.17,18,33,63,90 Osteoid osteoma may have a unique pathogenic nerve supply as well, a finding that may be common among bone tumors.53,65


Most cases of osteoid osteomas are stage 1 lesions because they resolve spontaneously. They can be treated symptomatically with aspirin or NSAIDs.8 If the patient fails nonsurgical treatment, surgical intervention is usually successful. If surgery is elected, it is important to eradicate the entire symptomatic nidus. Removal of a large amount of the surrounding sclerotic bone should be avoided because it can severely weaken the bone and may result in an iatrogenic pathologic fracture. For open techniques with regard to cortical lesions, adequate exposure is required to enable the surgeon to visualize the bulging cortex. Intralesional resection via the burr-down technique is generally preferred over en bloc resection. The nidus can be identified visually by the hyperemic pink color in the adjacent reactive bone. It is imperative to carry out curettage on the nidus followed by high-speed burring to advance the margin another 2 to 3 mm. If the lesion is not visible on the surface, which is usually the case in medullary lesions, radiographic markers should be placed intraoperatively prior to making the cortical window. Percutaneous radiofrequency ablation is another less invasive method of treating osteoid osteoma and is my preferred method of treatment (Fig. 148-2). This technique continues to gain wide acceptance as a preferable management modality.13,1921,47,76 Depending on location, CT guidance may be necessary, and is often extremely helpful to obtain successful eradication of the lesion.57 In cases in which there is an intra-articular lesion, arthroscopic treatment has been used successfully in adults and children.1,26,45,61






Osteofibrous Dysplasia


Osteofibrous dysplasia is a rare condition that is seen almost exclusively in the tibia of children younger than 10 years. It is more common in boys than in girls and is frequently asymptomatic. It commonly affects the diaphysis and results in anterior cortical bowing. However, it can occur in the fibula and can even be seen bilaterally in rare cases. True involvement of the knee is equally rare.


Radiographically, the lytic changes seen in the anterior tibial cortex are surrounded by sclerotic margins, creating a soap bubble appearance similar to the radiographic picture of fibrous dysplasia and adamantinoma. Some studies have suggested that osteofibrous dysplasia may be a precursor to adamantinoma.* Histologically, the lytic lesion shows a benign, trabecular, alphabet soup pattern in a fibrous stroma. The histologic findings are similar to those in fibrous dysplasia, although the lesions of fibrous dysplasia lack the prominent surface layer of rimming osteoblasts seen in osteofibrous dysplasia. The two can be distinguished by a variety of clinical, immunohistochemical,52,78 and molecular markers.79 These lesions are usually latent or active and, rarely, locally aggressive, because there is a relatively wide spectrum of disease.


Surgical treatment in osteofibrous dysplasia should be reserved for patients in whom the disease is poorly controlled with conservative treatment or those who have a high possibility of impending fracture and progression of their deformity.67 Early attempts at surgical curettage and grafting may result in a high failure rate because of recurrence. It is generally suggested that if intervention is necessary, it should be deferred until the patient reaches adolescence, when there is an improved chance that the disease may be arrested following surgery.88



Benign Cartilage-Forming Tumors



Enchondroma


An enchondroma refers to a centrally located benign cartilage neoplasm of medullary bone.50 These tumors are relatively common lesions, accounting for more than 10% of all benign bone tumors. Approximately 50% of cases arise in the small tubular bone of the hands and feet, with the next most common locations being the proximal humerus and distal femur. An enchondroma develops in a growing bone as a hamartomatous process. It is frequently asymptomatic and may avoid detection until the patient reaches adulthood. The lesion is usually discovered as an incidental finding on a routine radiographic examination, MRI for arthrographic examination or, more rarely, in association with a pathologic fracture.


Radiographs of enchondromas show geographic lysis of normal trabecular bone, with sharp margination and central stippled calcification (Fig. 148-3). Infrequently, there is associated pain, cortical scalloping, and dilation of the bone by a large tumor. When such features are present, one must be concerned about the possibility of a chondrosarcoma. Enchondromas are latent or active lesions.50 If a lesion is considered to be locally aggressive, it is much more likely to be chondrosarcoma, and referral for treatment is universally warranted.




Enchondromatosis, or Ollier’s disease, is a rare nonfamilial dysplasia with multiple enchondromas that is typically seen on half of the body and may be similar to fibrous dysplasia. When it is bilateral, one side tends to be more involved than the other. This condition can be extensive, with significant involvement of metaphyseal areas, resulting in bowing and shortening of the long bones (Fig. 148-4). Such dramatic changes are rarely seen in cases of a solitary enchondroma. Varus deformities can be severe and may be managed by a variety of techniques.16




A large solitary enchondroma in a large bone will convert to a low-grade chondrosarcoma in fewer than 5% of cases. If malignant transformation does occur, it will invariably take place during adulthood, and is very rarely in the short bones of the hands and feet. A secondary chondrosarcoma in enchondromatosis can arise in up to 20% of cases and may be related to inactivation of particular tumor suppressor genes.12


Patient with solitary enchondromas are treated symptomatically. If the patient has a pathologic fracture, it is usually best to allow the fracture to heal and perform a simple curettage and bone grafting procedure at a later date. This usually results in good function and a low chance of recurrence. Patients with Ollier’s disease or Maffucci’s disease (enchondromatosis associated with soft tissue hemangiomas) must be followed carefully because of the increased risk of malignant degeneration. This transformation usually occurs over a period of decades, and is more common in the long bones.1012




Osteochondroma


Solitary osteochondromas are the second most common benign tumor of bone after nonossifying fibromas. However, they are usually more symptomatic than nonossifying fibromas because of their location and morphology. For this reason, they are the most common benign tumor about the knee presenting to orthopedic surgeons and primary care physicians. Similar to an enchondroma, an osteochondroma is a developmental or hamartomatous process that arises from a defect in the outer edge of the metaphyseal side of the growth plate. This results in an exostosis that is directed opposite to the joint of origin as the lesion advances away from the growth plate during the growing years.


The three components of an osteochondroma include the cartilage cap, perichondrium, and bony stalk or base.74 The bony stalk of an osteochondroma is in direct communication with the medullary canal of the bone from which it arises, which is an essential component of correctly diagnosing these lesions. Osteochondromas can be pedunculated (narrow base), as is commonly seen around the knee (Fig. 148-6), or can be sessile (broad base). An associated cartilaginous cap on the bony base is required to make the diagnosis of osteochondroma. This cap has the histologic features of a normal growth plate during the growing years and is the only neoplastic portion of the osteochondroma. Osteochondroma growth plate activity subsides at the same time as the activity in the larger plate from which the osteochondroma arose.




A familial form of osteochondroma, multiple hereditary exostoses (MHE), is an autosomal dominant disorder that is 10% as common as a solitary osteochondroma, affecting 1 to 2 patients/100,000.83 Three genetic loci have been determined to be involved with MHE involving the EXT gene, the most common being EXT1 and EXT2. This condition can vary from mild to extensive and may involve symmetrical limb shortening and deformity in all extremities. Valgus knee deformity has been reported to be a common manifestation that may require corrective osteotomy.81 The metaphyseal portions of long bones are often deformed and widened (Fig. 148-7). The histologic findings in multiple exostoses are similar to those in solitary osteochondromas.




Conversion of a solitary osteochondroma to a chondrosarcoma occurs only during adulthood in less than 1% of cases. The overall rate of conversion for all types of solitary lesions is rare.40 In MEH, there is a 1% to 5% chance of malignant conversion to secondary chondrosarcoma especially in the larger, more proximal lesions (Fig. 148-8). However, this conversion rate is highly variable based on many years of literature reports.32




Solitary osteochondromas are latent lesions. Symptoms are caused secondary to mechanical effects on surrounding structures. Most children and adults with solitary osteochondromas are asymptomatic and therefore do not require surgical treatment. In some cases, the lesion may be palpable and irritating, as well as cosmetically unsettling.81 Surgical removal is appropriate in these cases to address the symptoms. Removal of the tumor as a prophylaxis for chondrosarcomatous degeneration is not recommended. Symptomatic lesions in patients with MHE are also addressed surgically as needed. Corrective osteotomy is occasionally required because of angulatory deformity about the knee—and loss of pronosupination of the forearm should be examined closely in children.


In adults with a solitary osteochondroma or with multiple exostoses, a previously quiescent lesion that begins to enlarge should be removed liberally. The surgical margin should be wide enough to include the entire cartilaginous cap because this is where malignant degeneration can occur.

Aug 26, 2016 | Posted by in ORTHOPEDIC | Comments Off on Surgical Treatment of Benign Bone Lesions
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